Effects of carbon sources on fungal morphology and lovastatin biosynthesis by submerged cultivation of Aspergillus terreus

Enhancing Monascus Pellet Formation for Improved Secondary Metabolite Production

Filamentous fungi are well-known for their ability to form mycelial pellets during submerged cultures, a characteristic that has been extensively studied and applied. However, Monascus, a filamentous saprophytic fungus with a rich history of medicinal and culinary applications, has not been widely documented for pellet formation. This study aimed to investigate the factors influencing pellet formation in Monascus and their impact on citrinin production, a key secondary metabolite. Through systematic exploration, we identified pH and inoculum size as critical factors governing pellet formation. Monascus exhibited optimal pellet growth within the acidic pH range from 5 to 6, resulting in smaller, more homogeneous pellets with lower citrinin content. Additionally, we found that inoculum size played a vital role, with lower spore concentrations favoring the formation of small, uniformly distributed pellets. The choice of carbon and nitrogen sources also influenced pellet stability, with glucose, peptone, and fishmeal supporting stable pellet formation. Notably, citrinin content was closely linked to pellet diameter, with larger pellets exhibiting higher citrinin levels. Our findings shed light on optimizing Monascus pellet formation for enhanced citrinin production and provide valuable insights into the cultivation of this fungus for various industrial applications. Further research is warranted to elucidate the molecular mechanisms underlying these observations.

Filamentous fungi for sustainable vegan food production systems within a circular economy: Present status and future prospects

Filamentous fungi serve as potential candidates in the production of different value-added products. In the context of food, there are several advantages of using filamentous fungi for food. Among the main advantages is that the fungal biomass used food not only meets basic nutritional requirements but that it is also rich in protein, low in fat, and free of cholesterol. This speaks to the potential of filamentous fungi in the production of food that can substitute animal-derived protein sources such as meat. Moreover, life-cycle analyses and techno-economic analyses reveal that fungal proteins perform better than animal-derived proteins in terms of land use efficiency as well as global warming. The present article provides an overview of the potential of filamentous fungi as a source of food and food supplements. The commercialization potential as well as social, legal and safety issues of fungi-based food products are discussed.

New knowledge about the biosynthesis of lovastatin and its production by fermentation of Aspergillus terreus

Lovastatin, and its semisynthetic derivative simvastatine, has great medical and economic importance, besides great potential for other uses. In the last years, a deeper and more complex view of secondary metabolism regulation has emerged, with the incorporation of cluster-specific and global transcription factors, and their relation to signaling cascades, as well as the new level of epigenetic regulation. Recently, a new mechanism, which regulates lovastatin biosynthesis, at transcriptional level, has been discovered: reactive oxygen species (ROS) regulation; also new unexpected environmental stimuli have been identified, which induce the synthesis of lovastatin, like quorum sensing-type molecules and support stimuli. The present review describes this new panorama and uses this information, together with the knowledge on lovastatin biosynthesis and genomics, as the foundation to analyze literature on optimization of fermentation parameters and medium composition, and also to fully understand new strategies for strain genetic improvement. This new knowledge has been applied to the development of more effective culture media, with the addition of molecules like butyrolactone I, oxylipins, and spermidine, or with addition of ROS-generating molecules to increase internal ROS levels in the cell. It has also been applied to the development of new strategies to generate overproducing strains of Aspergillus terreus, including engineering of the cluster-specific transcription factor (lovE), global transcription factors like the ones implicated in ROS regulation (or even mitochondrial alternative respiration aox gen), or the global regulator LaeA. Moreover, there is potential to apply some of these findings to the development of novel unconventional production systems. KEY POINTS: • New findings in regulation of lovastatin biosynthesis, like ROS regulation. • Induction by unexpected stimuli: autoinducer molecules and support stimuli. • Recent reports on culture medium and process optimization from this stand point. • Applications to molecular genetic strain improvement methods and production systems.

Influence of the construction of porous spargers on lovastatin production by Aspergillus terreus ATCC 20,542 in a laboratory bubble column

In bubble column bioreactors, the hydrodynamic behavior like mixing time, bubble size and morphology of filamentous fungi are influenced by the construction of spargers. Sparger pore size is an important factor influencing formation of bubbles. In this study for the first time, a 5-L bubble column bioreactor with different porous spargers was used to investigate the effect of mean air bubble diameter (at 0.36, 0.18 and 0.09 cm) on fungal growth, broth viscosity, fungal pellet morphology and lovastatin production by the filamentous fungus Aspergillus terreus. All cultivations were carried out at air flow rate equal to 0.5 L_air L^-1 min^-1. The viscosity of the broth was influenced by both biomass concentration and size of the fungal pellets. The highest values of viscosity were observed at bubbles of 0.09 cm diameter after 192 h of cultivation. The largest fluffy pellets and the highest yield of lovastatin (443 mg/L) were obtained at air bubbles diameter of 0.18 cm. Lovastatin yield on biomass growth in this condition was, respectively, 1.7-fold and 3.5-fold higher than in the cultivations performed with air bubbles of 0.36 and 0.09 cm diameters. These laboratory scale experiment indicates that air bubble diameter has the impact on lovastatin production and A. terreus culture conditions.

Enhanced biodiesel production through phyco-myco co-cultivation of Chlorella minutissima and Aspergillus awamori: An integrated approach

Algae-fungus co-culture was investigated as an alternative biodiesel feedstock. An oleaginous filamentous fungus Aspergillus awamori was co-cultured with Chlorella minutissima MCC 27 and Chlorella minutissima UTEX 2219, respectively in N11 medium furnished with different carbon and nitrogen sources. The biomass and lipid production potential of the two C. minutissima-A. awamori co-cultures was compared against the monocultures. A substantial enhancement in biomass and lipid accumulation was observed in both the co-cultures. When supplemented with different carbon and nitrogen sources, glycerol and potassium nitrate were found to be the most effective. In the presence of glycerol, a 2.6-3.9-fold increase of biomass and 3.4-5.1-fold increase of total lipid yields were observed in the co-cultures as compared to the axenic monocultures. Furthermore, C16:0 (31.26-35.02%) and C18:1 (21.14-24.21%) fatty acids were the major composites of the co-culture oils, which suggest co-culture as a promising strategy for biodiesel production.

Production of lovastatin and itaconic acid by Aspergillus terreus: a comparative perspective

Aspergillus terreus is a textbook example of an industrially relevant filamentous fungus. It is used for the biotechnological production of two valuable metabolites, namely itaconic acid and lovastatin. Itaconic acid serves as a precursor in polymer industry, whereas lovastatin found its place in the pharmaceutical market as a cholesterol-lowering statin drug and a precursor for semisynthetic statins. Interestingly, their biosynthetic gene clusters were shown to reside in the common genetic neighborhood. Despite the genomic proximity of the underlying biosynthetic genes, the production of lovastatin and itaconic acid was shown to be favored by different factors, especially with respect to pH values of the broth. While there are several reviews on various aspects of lovastatin and itaconic acid production, the survey on growth conditions, biochemistry and morphology related to the formation of these two metabolites has never been presented in the comparative manner. The aim of the current review is to outline the correlations and contrasts with respect to process-related and biochemical discoveries regarding itaconic acid and lovastatin production by A. terreus.

Mycelial pellet formation by edible ascomycete filamentous fungi, Neurospora intermedia

Pellet formation of filamentous fungi in submerged culture is an imperative topic of fermentation research. In this study, we report for the first time the growth of filamentous ascomycete fungus, Neurospora intermedia in its mycelial pellet form. In submerged culture, the growth morphology of the fungus was successfully manipulated into growing as pellets by modifying various cultivation conditions. Factors such as pH (2.0–10.0), agitation rate (100–150 rpm), carbon source (glucose, arabinose, sucrose, and galactose), the presence of additive agents (glycerol and calcium chloride) and trace metals were investigated for their effect on the pellet formation. Of the various factors screened, uniform pellets were formed only at pH range 3.0–4.0, signifying it as the most influential factor for N. intermedia pellet formation. The average pellet size ranged from 2.38 ± 0.12 to 2.86 ± 0.38 mm. The pellet formation remained unaffected by the inoculum type used and its size showed an inverse correlation with the agitation rate of the culture. Efficient glucose utilization was observed with fungal pellets, as opposed to the freely suspended mycelium, proving its viability for fast-fermentation processes. Scale up of the pelletization process was also carried out in bench-scale airlift and bubble column reactors (4.5 L).

Exploitation of Aspergillus terreus for the Production of Natural Statins

The fungus Aspergillus (A.) terreus has dominated the biological production of the “blockbuster” drugs known as statins. The statins are a class of drugs that inhibit HMG-CoA reductase and lead to lower cholesterol production. The statins were initially discovered in fungi and for many years fungi were the sole source for the statins. At present, novel chemically synthesised statins are produced as inspired by the naturally occurring statin molecules. The isolation of the natural statins, compactin, mevastatin and lovastatin from A. terreus represents one of the great achievements of industrial microbiology. Here we review the discovery of statins, along with strategies that have been applied to scale up their production by A. terreus strains. The strategies encompass many of the techniques available in industrial microbiology and include the optimization of media and fermentation conditions, the improvement of strains through classical mutagenesis, induced genetic manipulation and the use of statistical design.

Standardization of medium composition and agricultural waste in the production of p-hydroxybenzoic acid by Paecilomyces variotii

Biotransformation of p-coumaric acid by Paecilomyces variotii resulted in the accumulation of a metabolite which was identified as p-hydroxybenzoic acid. We studied the possibility of enhancing this metabolite by various parameters such as varying the concentration of substrate, addition of different nitrogen sources and carbon sources at varying concentration and use of different agricultural wastes as a nutritive medium. Maximum amount of 254.6 ± 9.34 mg/kg of p-hydroxybenzoic acid was detected in the solid medium of corncob on 4th day of incubation using 10 mM p-coumaric acid as a sole carbon source. Consequently, P. variotii can be used as candidate fungi for the production of p-hydroxybenzoic acid. Solid wastes can be managed by using them for biotransformation of pharmaceutically important phenolic acids and hence cut down the cost of production of value-added compounds using a low-cost medium.

Bioprocess Engineering Aspects of the Cultivation of a Lovastatin Producer Aspergillus terreus

The aim of this work is to review bioprocess engineering aspects of lovastatin (antihypercholesterolemia drug) production by Aspergillus terreus in the submerged culture in the bioreactors of various scale presented in the scientific literature since the nineties of the twentieth century. The key factor influencing the cultivation of any filamentous species is fungal morphology and that is why this aspect was treated as the starting point for further considerations. Fungal morphology is known to have an impact on the following issues connected with the cultivation of A. terreus reviewed in this article. These are broth viscosity in conjunction with non-Newtonian behaviour of the cultivation broths, and multistage oxygen transfer processes: from gas phase (air) to liquid phase (broth) and diffusion in the fungal agglomerates. The latest achievements concerning the controlling A. terreus morphology during lovastatin biosynthesis with the use of morphological engineering techniques were also reviewed. Last but not least, some attention was paid to the type of a bioreactor, its operational mode and kinetic modelling of lovastatin production by A. terreus.

Induction of a high-yield lovastatin mutant of Aspergillus terreus by ¹²C⁶⁺ heavy-ion beam irradiation and the influence of culture conditions on lovastatin production under submerged fermentation

Heavy-ion beams, possessing a wide mutation spectrum and increased mutation frequency, have been used effectively as a breeding method. In this study, the heavy-ion beams generated by the Heavy-Ion Research Facility in Lanzhou were used to mutagenize Aspergillus terreus CA99 for screening high-yield lovastatin strains. Furthermore, the main growth conditions as well as the influences of carbon and nitrogen sources on the growth and the lovastatin production of the mutant and the original strains were investigated comparatively. The spores of A. terreus CA99 were irradiated by 15, 20, 25, and 30 Gy of 80 MeV/u (12)C(6+) heavy-ion beams. Based on the lovastatin contents in the fermentation broth, a strain designated as A. terreus Z15-7 has been selected from the clone irradiated by the heavy-ion beam. When compared with the original strain, the content of lovastatin in the fermentation broth of A. terreus Z15-7 increased 4-fold. Moreover, A. terreus Z15-7 efficiently used the carbon and nitrogen sources for the growth and production of lovastatin when compared to the original strain. The maximum yield of lovastatin, 916.7 μg/ml, was obtained as A. terreus Z15-7 was submerged cultured in the chemically defined medium supplemented with 3% glycerol as a carbon source, 1% corn meal as an organic nitrogen source, and 0.2% sodium nitrate as an inorganic nitrogen source at 30 °C in the shake flask. The result shows that heavy-ion beam irradiation is an effective method for the mutation breeding of lovastatin production of A. terreus.